Continuous closed-loop power control system including modulation injection in a wireless transceiver power amplifier

ABSTRACT

A single continuous closed-loop power control feedback system provides seamless power control for a power amplifier and also enables an AM signal to be injected into the power amplifier through the power amplifiers&#39; control port. The AM signal is developed by an I/Q modulator and supplied to a comparator located in the power control loop. By using leakage from the power amplifier as feedback to a phase locked loop during initial power amplifier power ramp-up, the single continuous closed-loop power control system provides continuous feedback to the phase locked loop during the entire power amplification ramp-up period and eliminates the need for multiple feedback loops.

This application is a divisional of co-pending application Ser. No.09/704,930, filed on Nov. 2, 2000, the entire disclosure of which isincorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the versatile transmission of radio frequencypower in a wireless communication device transmitter, and moreparticularly, to a continuous closed-loop power control system includingmodulation injection into a wireless transceiver's power amplifier.

2. Related Art

With the increasing availability of efficient, low cost electronicmodules, mobile communication systems are becoming more and morewidespread. For example, there are many variations of communicationschemes in which various frequencies, transmission schemes, modulationtechniques and communication protocols are used to provide two-way voiceand data communications in a handheld telephone like communicationhandset. The different modulation and transmission schemes each haveadvantages and disadvantages.

As these mobile communication systems have been developed and deployed,many different standards, to which these systems must conform, haveevolved. For example, in the United States, portable communicationssystems complying with the IS-136 standard specify the use of aparticular modulation scheme and access format. In the case of IS-136,the modulation scheme can be 8-quadrature phase shift keying (8QPSK),offset π/4 differential quadrature phase shift keying (π/4-DQPSK) orvariations and the access format is time division multiple access(TDMA). Other standards may require the use of, for example, codedivision multiple access (CDMA).

Similarly, in Europe, the global system for mobile communications (GSM)standard requires the use of the gaussian minimum shift keying (GMSK)modulation scheme in a narrowband TDMA access environment.

Furthermore, in a typical GSM mobile communication system usingnarrowband TDMA technology, a GMSK modulation scheme supplies a veryclean phase modulated (PM) transmit signal to a non-linear poweramplifier directly from an oscillator. In such an arrangement, anon-linear power amplifier, which is highly efficient, can be used, thusallowing efficient transmission of the phase-modulated signal andminimizing power consumption. Because the modulated signal is supplieddirectly from an oscillator, the need for filtering, either before orafter the power amplifier, is minimized. Other transmission standards,such as that employed in IS-136, however, use a modulation scheme inwhich both a PM signal and an amplitude modulated (AM) signal aretransmitted. Standards such as these increase the data rate withoutincreasing the bandwidth of the transmitted signal. Unfortunately,existing GSM modulation schemes are not easily adapted to transmit asignal that includes both a PM component and an AM component. One reasonfor this difficulty is that in order to transmit a signal containing aPM component and an AM component, a highly linear power amplifier isrequired. Unfortunately, highly linear power amplifiers are veryinefficient, thus consuming significantly more power than a non-linearpower amplifier and drastically reducing the life of the battery orother power source.

This condition is further complicated because transmitters typicallyemployed in GSM communication systems transmit in bursts and must beable to control the ramp-up of the transmit power as well as have a highdegree of control over the output power level over a wide power range.In GSM this power control is typically performed using a closed feedbackloop in which a portion of the signal output from the power amplifier iscompared with a reference signal and the resulting error signal is fedback to the control port of the power amplifier.

When attempting to include a PM component and an AM component in a GSMtype modulation system, the power control loop will attenuate theamplitude variations present in the signal in an attempt to maintain aconstant output power. In such an arrangement, the power control looptends to cancel the AM portion of the signal.

In such systems in which transmit signals contain both PM and AMcomponents, the output power can be controlled by applying apre-determined control voltage to the power amplifier. Unfortunately,this requires the use of a highly linear, and therefore veryinefficient, power amplifier. In non-burst transmission systems theoutput power may be controlled by a feedback loop having a time-constantthat is very low compared to the time-constant of the amplitudevariations of the modulator. Another known method to control the outputpower is to “pre-distort” the modulated signal in such a way that thepower control loop will cancel the effect of the pre-distortion. In sucha method, the amplitude information is passed through a transferfunction that is the inverse of the power control loop transferfunction. Unfortunately, these methods are costly and inefficient.

Known multi-mode transmitter architectures require multiple variableelements, which are chosen depending upon the desired transmit mode.These architectures are complex, unreliable, require periodiccalibration, and cannot support multiple transmission standards withoutsignificant adjustments to the supporting analog and digital circuitry.

Further, in those transmission standards in which both a PM signal andan AM signal are sent to a power amplifier, unless the power amplifieris very linear, it may distort the combined transmission signal bycausing undesirable AM to PM conversion. This conversion is detrimentalto the transmit signal and can require the use of a costly andinefficient linear power amplifier.

With the increasing desirability of developing one worldwide portablecommunication standard, it would be desirable to have a multi-band andmulti-mode portable transceiver that can transmit a signal containingboth a PM component and an AM component, while maximizing the efficiencyof the power amplifier. Furthermore, it would be desirable to have sucha multi-band and multi-mode portable transceiver that can useconventional in-phase (I) and quadrature (Q) transmit signal componentswithout requiring separate baseband signals for phase modulation andamplitude modulation. Further still, as the GSM standard evolvesfurther, such as with the development of enhanced data rates for GSMevolution (EDGE), it is desirable to have one portable transceiver thatmay operate in all systems.

SUMMARY

The invention provides a continuous closed-loop power control system,which includes modulation injection into a wireless transceiver's poweramplifier that allows the use of non-linear, power efficient amplifiers.The invention uses a single continuous closed-loop power control systemthat allows an AM signal to be injected into the power amplifier throughthe power amplifier control port. The AM signal is derived from theoutput of an I/Q modulator and supplied to a comparator located withinthe power control feedback loop. By using the leakage from the poweramplifier as feedback to a translation loop during the initial poweramplifier ramp-up, continuous phase feedback to the translation loop isachieved during the entire power amplification ramp-up period, thuseliminating the need for multiple feedback loops.

Related methods of operation and computer readable media are alsoprovided. Other systems, methods, features, and advantages of theinvention will be or become apparent to one with skill in the art uponexamination of the following figures and detailed description. It isintended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE FIGURES

The components in the figures are not necessarily to scale, emphasisinstead being placed upon illustrating the principles of the invention.Moreover, in the figures, like reference numerals designatecorresponding parts throughout the different views.

FIG. 1 is a block diagram illustrating a simplified portabletransceiver.

FIG. 2 is a block diagram illustrating the upconverter and power controlelement of FIG. 1 including the continuous closed-loop power controlsystem of the invention.

FIG. 3 is a graphical representation of the average power output of thepower amplifier of FIG. 2.

FIG. 4 is a schematic view illustrating an alternative embodiment of thepower amplifier circuit of FIG. 2.

FIG. 5 is a schematic view illustrating another alternative embodimentof the power amplifier circuit of FIG. 2.

DETAILED DESCRIPTION

Although described with particular reference to a portable transceiver,the continuous closed-loop power control system including modulationinjection can be implemented in any system where it is desirable totransmit a combined signal including a PM component and an AM component.Furthermore, the continuous closed-loop power control system can beimplemented independently from the modulation injection, where bothsystems are applicable to any system where it is desirable to implementa closed power control feedback loop and where a PM signal and an AMsignal are amplified by a power amplifier.

Further still the continuous closed-loop power control system includingmodulation injection can be implemented in software, hardware, or acombination of hardware and software. In a preferred embodiment(s),selected portions of the continuous closed-loop power control systemincluding modulation injection are implemented in hardware and software.The hardware portion of the invention can be implemented usingspecialized hardware logic. The software portion can be stored in amemory and be executed by a suitable instruction execution system(microprocessor). The hardware implementation of the continuousclosed-loop power control system including modulation injection caninclude any or a combination of the following technologies, which areall well known in the art: a discrete logic circuit(s) having logicgates for implementing logic functions upon data signals, an applicationspecific integrated circuit having appropriate logic gates, aprogrammable gate array(s) (PGA), a field programmable gate array(FPGA), etc.

Furthermore, the continuous closed-loop power control system includingmodulation injection software, which comprises an ordered listing ofexecutable instructions for implementing logical functions, can beembodied in any computer-readable medium for use by or in connectionwith an instruction execution system, apparatus, or device, such as acomputer-based system, processor-containing system, or other system thatcan fetch the instructions from the instruction execution system,apparatus, or device and execute the instructions.

In the context of this document, a “computer-readable medium” can be anymeans that can contain, store, communicate, propagate, or transport theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The computer readable medium can be, forexample but not limited to, an electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system, apparatus, device,or propagation medium. More specific examples (a nonexhaustive list) ofthe computer-readable medium would include the following: an electricalconnection (electronic) having one or more wires, a portable computerdiskette (magnetic), a random access memory (RAM), a read-only memory(ROM), an erasable programmable read-only memory (EPROM or Flash memory)(magnetic), an optical fiber (optical), and a portable compact discread-only memory (CDROM) (optical). Note that the computer-readablemedium could even be paper or another suitable medium upon which theprogram is printed, as the program can be electronically captured, viafor instance optical scanning of the paper or other medium, thencompiled, interpreted or otherwise processed in a suitable manner ifnecessary, and then stored in a computer memory.

FIG. 1 is a block diagram illustrating a simplified portable transceiver100. Portable transceiver 100 includes speaker 102, display 104,keyboard 106, and microphone 108, all connected to baseband subsystem110. In a particular embodiment, portable transceiver 100 can be, forexample but not limited to, a portable telecommunication handset such asa mobile cellular-type telephone. Speaker 102 and display 104 receivesignals from baseband subsystem 110 via connections 112 and 114,respectively, as known to those skilled in the art. Similarly, keyboard106 and microphone 108 supply signals to baseband subsystem 110 viaconnections 116 and 118, respectively. Baseband subsystem 110 includesmicroprocessor (μP) 120, memory 122, analog circuitry 124, and digitalsignal processor (DSP) 126 in communication via bus 128. Bus 128, thoughshown as a single bus, may be implemented using a number of bussesconnected as necessary among the subsystems within baseband subsystem110. Microprocessor 120 and memory 122 provide the signal timing,processing and storage functions for portable transceiver 100. Analogcircuitry 124 provides the analog processing functions for the signalswithin baseband subsystem 110. Baseband subsystem 110 provides controlsignals to radio frequency (RF) subsystem 130 via connection 132.Although shown as a single connection 132, the control signals mayoriginate from DSP 126 or from microprocessor 120, and are supplied to avariety of points within RF subsystem 130. It should be noted that, forsimplicity, only the basic components of portable transceiver 100 areillustrated.

Baseband subsystem 110 also includes analog-to-digital converter (ADC)134 and digital-to-analog converters (DACs) 136 and 142. ADC 134 andDACs 136 and 142 also communicate with microprocessor 120, memory 122,analog circuitry 124 and DSP 126 via bus 128. DAC 136 converts thedigital communication information within baseband subsystem 110 into ananalog signal for transmission to RF subsystem 130 via connection 140.Connection 140, while shown as two directed arrows, includes theinformation that is to be transmitted by RF subsystem 130 afterconversion from the digital domain to the analog domain. In accordancewith an embodiment of the invention, DAC 136 supplies baseband in-phase(I) and quadrature (Q) components of the information signal to betransmitted via connection 140 to modulator 146. In such an embodiment,modulator 146 is an I/Q modulator. DAC 142 supplies control signals tovarious components with RF subsystem 130 via connection 132.

Modulator 146, after receiving a frequency reference signal, also calleda “local oscillator,” signal, or “LO,” from synthesizer 148 viaconnection 150, modulates the I and Q information signals received fromthe DAC 136 onto the LO signal and provides a modulated signal viaconnection 152 to upconverter 154. Modulator 146 also supplies anintermediate frequency (IF) signal containing only the desired amplitudemodulated (AM) signal component on connection 138 for input to the powercontrol element 300 via connection 138. The power control element 300also supplies to the modulator 146 via connection 144 a constant levelIF signal containing both the phase modulated (PM) and AM components ofthe transmit signal. The operation of the power control element 300 willbe described below with reference to FIG. 2.

Upconverter 154 also receives a frequency reference signal fromsynthesizer 148 via connection 156. Synthesizer 148 determines theappropriate frequency to which upconverter 154 will upconvert themodulated signal on connection 152.

Upconverter 154 supplies the fully modulated signal at the appropriatetransmit frequency via connection 158 to power amplifier 160. Poweramplifier 160 amplifies the modulated signal on connection 158 to theappropriate power level for transmission via connection 162 to antenna164. Illustratively, switch 166 controls whether the amplified signal onconnection 162 is transferred to antenna 164 or whether a receivedsignal from antenna 164 is supplied to filter 168. The operation ofswitch 166 is controlled by a control signal from baseband subsystem 110via connection 132.

A portion of the amplified transmit signal power on connection 162 issupplied via connection 170 to power control element 300. Power controlelement 300 forms a continuous closed power control feedback loop andsupplies an information signal on connection 172 instructing the poweramplifier 160 as to the power to which the signal on connection 158should be amplified. The power control element 300 also receives the LOsignal from synthesizer 148 via connection 198. The operation of powercontrol element 300 will be described in further detail with respect toFIG. 2.

A signal received by antenna 164 may, at the appropriate time determinedby baseband subsystem 110, be directed via switch 166 to receive filter168. Receive filter 168 will filter the received signal and supply thefiltered signal on connection 174 to low noise amplifier (LNA) 176.Receive filter 168 may be a bandpass filter that passes all channels ofthe particular cellular system where the portable transceiver 100 isoperating. As an example, for a 900 MHz GSM system, receive filter 168would pass all frequencies from 935.1 MHz to 959.9 MHz, covering all 124contiguous channels of 200 kHz each. The purpose of this filter is toreject all frequencies outside the desired region. LNA 176 amplifies thevery weak signal on connection 174 to a level at which downconverter 178can translate the signal from the transmitted frequency back to abaseband frequency. Alternatively, the functionality of LNA 176 anddownconverter 178 can be accomplished using other elements, such as, forexample but not limited to, a low noise block downconverter (LNB).

Downconverter 178 receives an LO signal from synthesizer 148, viaconnection 180. The LO signal determines the frequency to which todownconvert the signal received from LNA 176 via connection 182. Thedownconverted frequency is called the intermediate frequency (IF).Downconverter 178 sends the downconverted signal via connection 184 tochannel filter 186, also called the “IF filter.” Channel filter 186filters the downconverted signal and supplies it via connection 188 toamplifier 190. The channel filter 186 selects the one desired channeland rejects all others. Using the GSM system as an example, only one ofthe 124 contiguous channels is actually to be received. After allchannels are passed by receive filter 168 and downconverted in frequencyby downconverter 178, only the one desired channel will appear preciselyat the center frequency of channel filter 186. The synthesizer 148, bycontrolling the local oscillator frequency supplied on connection 180 todownconverter 178, determines the selected channel. Amplifier 190amplifies the received signal and supplies the amplified signal viaconnection 192 to demodulator 194. Demodulator 194 recovers thetransmitted analog information and supplies a signal representing thisinformation via connection 196 to ADC 134. ADC 134 converts these analogsignals to a digital signal at baseband frequency and transfers it viabus 128 to DSP 126 for further processing.

FIG. 2 is a block diagram illustrating the upconverter 154 and powercontrol element 300 of FIG. 1 including the continuous closed-loop powercontrol system and modulation injection of the invention. Beginning witha description of the power control loop 300, a portion of the outputpower present at the output of power amplifier 160 on connection 162 isdiverted by coupler 222 via connection 170 and input to mixer 226 in thepower control element 300. Mixer 226 also receives the local oscillator(LO) signal from synthesizer 148 via connection 198.

The mixer 226 down converts the RF signal on connection 170 to anintermediate frequency (IF) signal on connection 228. For example, mixer226 takes a signal having a frequency of approximately 2 gigahertz (GHz)on connection 170 and down converts it to a frequency of approximately100 megahertz (MHz) on connection 228 for input to variable gain element232. Variable gain element 232 can be, for example but not limited to, avariable gain amplifier or an attenuator. In such an arrangement,variable gain element 232 might have a dynamic range of approximately 70decibels (dB) i.e., +35 dB/−35 dB. Variable gain element 232 receives acontrol signal input from the non-inverting output of amplifier 236 viaconnection 234. The input to amplifier 236 is supplied via connection132 from the DAC 142 of FIG. 1. The signal on connection 132 is areference voltage signal for the transmit power level and provides thepower profile. This signal on connection 132 is supplied to areconstruction filter, which includes resistor 240 and capacitor 242. Inthis manner, a reference voltage for the transmit power level and powerprofile is supplied via connection 234 to the control input of thevariable gain element 232.

The output of variable gain element 232 on connection 246 is at an IFand includes modulation having both an AM component and a PM componentand is called the “power measurement signal.” This power measurementsignal is related to the absolute output power of power amplifier 160,and includes a very small error related to the AM and PM componentspresent in the signal. The output of variable gain element 232 onconnection 246 is supplied to the input of power detector 262 and isalso supplied to a limiter 248 in the phase locked loop 220. The IFsignal on connection 246 includes both an AM component and a PMcomponent. The signal on connection 246 is supplied to power detector262, which provides, on connection 264, a baseband signal representingthe instantaneous level of IF power present on connection 246. Theoutput of power detector 262 on connection 264 is supplied to theinverting input of amplifier 268.

Amplifier 268, capacitor 266 and capacitor 270 form a comparator 284,which provides the error signal used to control the power amplifier 160via connection 272. The non-inverting input to the amplifier 268 issupplied via connection 138 from the output of the modulator 146 throughthe power detector 276. The signal on connection 138 supplied to thenon-inverting input of amplifier 268 contains the AM modulationdeveloped by the modulator 146 in the phase locked loop 220 for input tothe control port 172 of power amplifier 160.

The gain of the power control loop 300 amplifies the signal onconnection 272 such that the difference between the signals onconnections 264 and 138 input to amplifier 268 provide an error onconnection 272 that is used to control the output of the power amplifier160. The error on connection 272 is supplied to variable gain element274, which can be similar in structure to variable gain element 232.However, the variable gain element 274 has a function that is inverse tothat of variable gain element 232. The control input to variable gainelement 274 is supplied from the inverting output of amplifier 236. Inthis manner, the power amplifier control signal on connection 172supplied to the control port of power amplifier 160 drives the poweramplifier 160 to provide the proper output on connection 162.

The level of the signal on connection 264 and the level of the signal onconnection 138 should be equal. For example, if the output level of thevariable gain element 232 is increased by a factor of 10, then the levelof the output of power amplifier 160 should be decreased accordingly tomaintain equilibrium at the input of the amplifier 268. The output ofthe power amplifier 160 changes to cancel the gain change of variablegain element 232. In this manner, the amplitude of the signal onconnection 264 remains equal to the amplitude of the signal onconnection 138. However, this implies that the signal on connection 228lags the signal on connection 234 with the result that the two signalswill not completely cancel. In this manner, an error signal with an AMand a PM portion is present on connection 246. The signal on connection246 is converted by power detector 262 from an IF signal to a basebandsignal on connection 264. The signal on connection 264 is amplified byamplifier 268 and amplifier 274 to drive the power amplifier controlport on connection 172 so that the desired signal is achieved at theoutput of the power amplifier 160 on connection 162. Power control loop300 has sufficient gain so that the error signal on connection 264 canbe kept small. In such a case, the gain changes of variable gain element232 and the power amplifier 160 will substantially be the inverse ofeach other.

In addition to amplifying the error signal on connection 264, theamplifier 268 also compares the power measurement signal on connection264 with a reference voltage signal including an AM portion onconnection 138, supplied by the modulator 146 within the phase lockedloop 220. The DC voltage level on connection 138 affects the desiredstatic output power for the power amplifier 268, irrespective of AMmodulation. Amplifier 268 compares the signal level on connection 264with the signal level on connection 138 and then amplifies thedifference, thus providing a power control signal on connection 272. Thecomparator 284 functions as an integrator, which is also a low passfilter.

The power control signal on connection 272 drives the variable gainamplifier 274, which corrects for the effect that variable gain element232 has on the transfer function of power control loop 300. The variablegains of variable gain element 232 and variable gain element 274 arecomplimentary. Because the power measurement signal is present onconnection 264 and the AM error signal is present on connection 138, theamplifier 268 provides a dual function; (1) it amplifies the AM errorsignal on connection 138 so as to modulate the power output of poweramplifier 160 via connection 172 to have the correct amount of AM; and(2) it performs the average power comparison and amplifies the result,thus providing a control signal on connection 272 that drives the poweramplifier 160 to the correct average power output. Therefore, atconnection 172 both the AM error signal and the power control errorsignal are amplified to a level sufficient to drive the power amplifier160 to the desired average power with the desired AM signal. In thismanner, the desired AM portion of the signal is supplied to the controlinput 172 of power amplifier 160 and made present on the power amplifieroutput on connection 162. Mixer 226, variable gain element 232, powerdetector 262, amplifier 268 and variable gain element 274 provide acontinuous closed-loop power control feedback system to control thepower output of power amplifier 160, while allowing for the introductionof the AM portion of the transmit signal via connection 138.

At all times, the continuous power-control feedback loop allows thecorrection of any phase shift caused by power amplifier 160. In thismanner, the PLL 220 now includes a feedback loop for looping back theoutput of power amplifier 160 to the input of phase/frequency detector208. Any unwanted phase shift generated by the power amplifier 160 willbe corrected by the PLL 220. The output of variable gain element 232passes any phase distortion present via connection 246 to limiter 248for correction by the PLL 220. As such, the phase of the output of poweramplifier 160 is forced to follow the phase of the LO signal onconnection 156.

In order to remove the AM from the output of variable gain element 232,the variable gain element 232 is connected via connection 246 andconnection 144 to the input of limiter 248. Limiter 248 develops a localoscillator signal containing only a PM component on connection 250. ThisLO signal is supplied via connection 250 to the modulator 146. Inaddition, the baseband I and Q information signals are supplied viaconnections 278 and 282, respectively, to the modulator 146. The I and Qbaseband information signal interface is understood by those havingordinary skill in the art. As a result of the operation of the modulator146, the output on connection 252 is an intermediate frequency signalincluding an AM component in the form of an AM reference signal and asmall PM error signal. The output of modulator 146 is supplied viaconnection 252 to power detector 276. In this manner, the output ofpower detector 276 also includes the AM portion of the desired transmitsignal. In this manner, the signal provided on connection 138 is areference signal for input to the power control loop 300. Because thepower control loop 300 has limited bandwidth, the rate at which theamplitude modulation occurs on connection 138 is preferably within thatpower control loop bandwidth.

The output of limiter 248 is supplied via connection 250 as a localoscillator signal having a PM component, but substantially no AMcomponent to the modulator 146. The modulator 146 removes virtually theentire PM component and applies an AM modulated component to the signaland supplies this signal via connection 252. In order to remove the PMcomponent present on connection 250, the I and Q signals are reversed onconnections 278 and 282, respectively. In this manner, the output ofmodulator 146 on connection 252 contains a very small PM portion and asignificant AM portion. With respect to the PM component of the signalon connection 252, the modulator 146 acts as a comparator, comparing theI and Q signals on connections 278 and 282, respectively, with the LOsignal supplied from the output of the variable gain element 232,through limiter 248 and on connection 250. The components within thephase locked loop 220 provide gain for the comparison of the PM onconnection 250 and the modulator connections 278 and 282, thus providinga phase error output of the modulator 146 on connection 252. This phaseerror signal is then supplied to limiter 256, which outputs a signal onconnection 258 containing the small PM phase error component.

In this manner, a feedback signal taken from the output of variable gainelement 232 on connection 246 is supplied as continuous feedback to thephase locked loop 220. The error signal output of modulator 146 onconnection 252 containing the phase error, will get smaller and smalleras the gain of the phase locked loop 220 increases. However, there willalways be some error signal present, thus enabling the phase locked loop220 to achieve phase lock. It should be noted that even when the poweramplifier 160 is not operating, there will always be some small leakagethrough the power amplifier 160 onto connection 162. This small leakageis sufficient to provide a feedback signal through the variable gainelement 232 and into the phase locked loop 220 such that the phaselocked loop 220 can be locked using just the leakage output of poweramplifier 160. In this manner, a single feedback loop can be used tocontinuously control the output power of power amplifier 160 from thetime that the amplifier is off through the time when the amplifier 160is providing full output power.

Phase/frequency detector 208 receives an unmodulated input signal fromsynthesizer 148 via connection 156. The unmodulated input signal isfrequency divided by a number “x” in order to provide a signal having anappropriate frequency on connection 204. The number “x” is chosen so asto minimize the design complexity of the synthesizer 148 and can be, forexample, but not limited to, chosen to convert the output of thesynthesizer 148 to a frequency of 100 MHz. Phase/frequency detector 208also receives the output of divider 260 via connection 206. The number“y” is chosen in similar manner to that of the number “x.”Phase/frequency detector 208 detects any phase difference between thesignal on connection 204 and the signal on connection 206 and places asignal on connection 210 that has an amplitude proportional to thedifference. When the phase difference reaches 360°, the output ofphase/frequency detector 208 on connection 210 will become proportionalto the frequency difference between the signals on connections 204 and206.

The output of phase/frequency detector 208 on connection 210 is adigital signal having a value of either a 0 or a 1 with a very smalltransition time between the two output states. This signal on connection210 is supplied to low-pass filter 212, which integrates the signal onconnection 210 and places a DC signal on connection 214 that controlsthe frequency of the transmit voltage control oscillator (TX VCO) 216.The output of TX VCO 216 is supplied via connection 158 directly to thepower amplifier 160. In this manner, the synthesizer 148, limiter 248,modulator 146, limiter 256, divider 260, divider 202, phase/frequencydetector 208, low-pass filter 212 and TX VCO 216 form a phase lockedloop (PLL) 200, which is used to determine the transmit frequency onconnection 158. When the PLL 220 is settled, or “locked,” then the twosignals entering the phase/frequency detector 208 on connections 204 and206 have precisely the same phase and frequency, and the output of thephase/frequency detector 208 on connection 210 goes to zero. The outputof the integrating low-pass filter 212 on connection 214 stabilizes,resulting in a fixed frequency out of TX VCO 216. For example, thesynthesizer 148 and the mixer 226 ensure that the frequency of thesignal output from the TX VCO 216 on connection 158 tracks the sum ofthe frequencies of the local oscillator signal supplied by synthesizer148 and the IF frequency on connection 206.

When the phase locked loop 220 is locked, the phase of the signal oilconnection 204 and the phase of the signal on connection 206 will beequal. Because the amount of PM on connection 206 should be very small,the gain in the phase locked loop 220 has to be sufficiently high toamplify the error signal on connection 206 to a level at which thephase/frequency detector 208 can make a comparison. By using themodulator 146 to impose the I and Q information signals on the signal onconnection 250 in a direction opposite from which it is desirable forthe phase of the TX VCO to move, and because it is desirable for thephase locked loop 220 to remain locked, the phase of the signal outputfrom the TX VCO 216 on connection 158 will move opposite that of thephase imposed by the modulator 146. In this manner, the PM error signalpresent on connection 206 is minimized by the very high sensitivity, ofthe order of many MHz per volt, of the TX VCO 216.

Because the power control loop 300 is a closed loop for AM signals atconnection 138, it is possible to use a non-linear, and therefore highlyefficient, power amplifier 160. Furthermore, the undesirable anddetrimental AM-to-PM conversion, which occurs due to the amplitudedependence of an amplifier's phase shift, is rectified by the poweramplifier 160 being included within the phase locked loop 220. Byseparating the AM and the PM modulation and by providing closed loopcontrol for both the AM and PM modulation, a non-linear, and thereforehighly efficient power amplifier can be used.

In some applications it is desirable to allow the power amplifier 160 tooutput a signal containing both an AM component and a PM component,while maintaining the power amplifier 160 as a non-linear (and thereforehighly efficient) power amplifier. In such a case, the output ofmodulator 146 will include both a very small AM and PM component, withlimiter 256 used to cancel the AM component present on connection 252,thereby preventing any AM-to-PM conversion in the phase/frequencydetector 208.

FIG. 3 is a graphical representation of the average power output ofpower amplifier 160 of FIG. 2. The vertical axis of graph 350 representsaverage power output of the power amplifier 160 and the horizontal axisof graph 350 represents time. Point “a” represents the point in time atwhich a transmission burst is initiated. At this time leakage from thepower amplifier 160 is used to provide feedback from the variable gainelement 232 (FIG. 2) to the phase locked loop 220 (FIG. 2) with thevariable gain element 232 set to maximum gain. During the followingramp-up time the PLL 220 of FIG. 2 tracks the output of the poweramplifier 160 with the gain of variable gain element 232 (and thereforethe amplitude fed back to phase locked loop 220) reducing as the rampprogresses in time, thus allowing the PLL 220 to correct any phasedistortion present at the output of power amplifier 160. The point “c”in FIG. 3 represents the point at which the power amplifier 160 hasdeveloped sufficient power so that transmission of data may begin. Inthis manner, a single power control loop provides continuous powerdetection and feedback to the PILL 220.

FIG. 4 is a schematic view illustrating an alternative embodiment 400 ofthe power amplifier circuit of FIG. 2. In some applications it may bedesirable to have the ability to transmit an AM signal having a verywide bandwidth. Therefore, and in a departure from that discussed abovewith respect to FIG. 2, the power amplifier circuit 400 of FIG. 4includes a mixer 492 added to the phase locked loop 420. The mixer 492receives the output of the TX VCO 416 on connection 494 and alsoreceives as input the output of a low-pass filter 490 via connection496.

To develop the signal for input to the mixer 492, the output ofmodulator 446 on connection 452 is supplied to mixer 480. Mixer 480combines the PM component of the signal on connection 458 with the AMcomponent of the signal on connection 452. The mixer 480 combines thesignal on connection 452 containing the AM and very small PM componentand the signal on connection 458 containing the very small PM component,and combines them, thus extracting the AM signal and placing it onconnection 484. The AM signal on connection 484 is at a basebandfrequency and is supplied to amplifier 4.86. Amplifier 486 scales thesignal on connection 484 and supplies the scaled signal, via connection488, to low-pass filter 490. The AM slope information is supplied to thecontrol input to the amplifier 486 from the DAC 142 via connection 132(FIG. 1). Low-pass filter 490 removes any high frequency components fromthe signal on connection 488 and supplies the AM signal via connection496 to the mixer 492.

The mixer 492 combines the AM signal on connection 496 with the PMsignal supplied from the TX VCO 416 on connection 494 and supplies acombined modulated signal containing both AM and PM on connection 458.This combined signal is then supplied to the power amplifier 160.

With respect to the power control loop 400, as described above, areference voltage signal containing the AM signal component is suppliedfrom the output of the modulator 446 via connection 438 to thenon-inverting input of amplifier 468 in the comparator 484. The signalsupplied from power detector 462 via connection 464 contains an AMcomponent. Because the AM signal component on connection 464 is in phasewith respect to the AM signal component on connection 438, the two AMcomponents will substantially cancel in the comparator 484, thuseliminating the AM portion of the signal from the output of amplifier468 on connection 472. The output of amplifier 468 on connection 472 isthe error signal used to adjust the output power of power amplifier 160as described above.

FIG. 5 is a schematic view illustrating another alternative embodiment500 of the power amplifier circuit of FIG. 2. The power amplifiercircuit 500 includes power control loop 500, where modulator 546 isplaced at the output of variable gain element 532. The input signal tomodulator 546 on connection 538 is a constant level signal supplied byvariable gain element 532. The output of variable gain element 532includes both an AM and PM component. The baseband I and Q informationsignals are supplied to the modulator 546 via connections 578 and 582,respectively.

With respect to the PM signal on connection 538, when a PM signal issupplied to modulator 546, the I and Q components will remove, orgreatly reduce the level of the PM signal on connection 538 within theloop bandwidth of phase locked loop 520. With respect to the AM portionof the signal on connection 538, the I and Q positions will also reducethe AM component by a function equal to the gain of the power controlloop 500. Therefore, the value of the AM and PM components at the outputof modulator 546 on connection 550 are very small error signals asmentioned above. In accordance with this aspect of the invention, theinverse of the I and Q information signals are supplied to the modulator546 on connections 578 and 582, respectively, thus providing the errorsignal on connection 550. The error signal on connection 550 includesboth PM and AM components.

This small error signal is supplied on connection 550 to thephase/frequency detector 508, which, because there is virtually no AMpresent on the signal on connection 550, will measure the phasedifference between the signal on connection 550 and the signal onconnection 504. The phase/frequency detector 508 provides a signal onconnection 510 as described above with respect to FIG. 2.

The error signal on connection 550 is also supplied to power detector562, which converts the IF signal on connection 550 to a DC plus smallAM error signal on connection 564, the DC component representing theaverage power output of power amplifier 160. The signal on connection564 is supplied to the inverting input of amplifier 568. Thenon-inverting input to amplifier 568 is coupled from a common modevoltage signal V_(REF). Amplifier 568 functions as a phase inverter,thus inverting the phase of the signal on connection 564 and supplyingthis inverted phase signal as a power amplifier control signal onconnection 572. The control signal on connection 572 is supplied tovariable gain element 574, which functions similar to the variable gainelement 274 of FIG. 2. The variable gain element 574 supplies a controloutput to the power amplifier 160 via connection 172.

Advantageously, the embodiment illustrated in FIG. 5 eliminates one ofthe power 2 c detectors (power detector 276) shown in FIG. 2. In thismanner, it is unnecessary to match the operational characteristics ofthe power detector 276 and the power detector 262 of FIG. 2.Furthermore, the limiters 248 and 256 of FIG. 2 are also eliminated.

While various embodiments of the invention have been described, it willbe apparent to those of ordinary skill in the art that many moreembodiments and implementations are possible that are within the scopeof this invention Accordingly, the invention is not to be restrictedexcept in light of the attached claims and their equivalents.

1. A power amplifier control circuit, comprising: a power amplifier; apower control loop coupled to the power amplifier; and a phase lockedloop coupled to the power control loop, where the power control loopprovides a feedback signal to the phase locked loop, the feedback signalderived using leakage from the power amplifier during a time when thepower amplifier is not operating.
 2. The circuit of claim 1, wherein thepower control loop provides a feedback signal to the phase locked loop,the feedback signal derived from the output power of the power amplifierduring a time when the power amplifier is operating.
 3. A method foroperating a power amplifier, the method comprising the steps of:providing a power amplifier and a power control loop; developing afeedback signal in the power control loop; and providing the feedbacksignal to a phase locked loop, the feedback signal derived using leakagefrom the power amplifier during a time when the power amplifier is notoperating.
 4. The method of claim 3, further comprising the step ofderiving the feedback signal from the output power of the poweramplifier during a time when the power amplifier is operating.
 5. Acomputer readable medium having a program for operating a poweramplifier, the program comprising logic for performing the steps of:providing a power amplifier and a power control loop; developing afeedback signal in the power control loop; and providing the feedbacksignal to a phase locked loop, the feedback signal derived using leakagefrom the power amplifier during a time when the power amplifier is notoperating.
 6. The program of claim 5, further comprising logic forperforming the step of deriving the feedback signal from the outputpower of the power amplifier during a time when the power amplifier isoperating.